1. Field of the Invention
The invention relates to agitators or circulators for inducing currents—or waves if that is preferred—in a given tank. One example illustrative use environment for the invention involves salt water aquariums in which it is desirable to generate a wave and/or current environment similar to an actual reef so that filter-feeding organisms like coral are given plenty of plankton circulated by them to feed on. Other example use environments include without limitation process industries like the chemical, food, or water treatment industries and so on, for use in mixing tanks to mix dissolving chemicals or blend fluids or the like, including suspending or dispersing particles, bubbles, droplets, fluid clumps and so on.
Additional aspects and objects of the invention will be apparent in connection with the discussion further below of preferred embodiments and examples.
2. Prior Art
Waves at the surface of fluids appear as a variation of the familiar sine curve in mathematics. The amplitude and frequency of the wave are analogous to its mathematical counterpart. The amplitude of a surface wave can be best described as the height of the crest of the wave. The period of the wave is the time in seconds for successive crests to pass a fixed point. The frequency of the wave is the inverse of the period. The amplitude of the wave (height of the crests) is directly proportional to the force with which the water/fluid hits stationary objects. Waves with large crests (amplitude) carry a large volume of water which, when decelerated by stationary objects, produce large forces. Correspondingly, waves with small amplitudes produce small forces.
Surface waves in nature, aquariums and tanks vary from the sine analogy in that they are three dimensional. Surface waves in nature have eddy currents, back pressure from the previous wave meeting the shore or reef, undercurrents, etc., which change the shape, amplitude and frequency of the wave.
Waves below the surface can be described as an increasing and a decreasing of the mass flow rate through a given volume of fluid. This increasing and decreasing of flow requires a corresponding increasing and decreasing of pressure. The amplitude of the wave can be described as the flow rate over a given volume. The period is the time needed for the flow to switch from ON to OFF and back ON. The flow can also be pulsed from high to low. As previously stated, the frequency is the inverse of the period.
For surface and below surface waves, the fluid carries energy which can be dissipated in many ways. Two of the more prominent are:—(i) the energy is dissipated in the fluid by shear, and (ii) the energy is dissipated in the fluid by contact with a stationary object. In the ocean, stationary objects include irregular terrain, ocean floor, boulders, vegetation, shoreline, and so on. In a tank, stationary objects include the sides, bottom, bulkheads, fixtures, and so on. Steady streams also loose energy by shear or by contact with stationary objects. Most of the energy losses in a steady stream occur at the boundaries of the flow.
The dissipation of energy in large volumes of fluid, whether from a wave or a stream, causes turbulence. Turbulence along with a substantial flow rate are the desired components for a thriving aquarium or for an efficient fluid mixer.
In tank environments, pumping operations, engines, fuel systems, hydraulic systems or any fluidized system, filters are generally used to remove sediment, waste, debris, impurities, and so on. Most filters use a meshed media to trap particles of a certain size. The smaller the opening or pore, the smaller the particle it can retain. As filters trap particles, the available area to pass fluid is reduced. When this happens, the flow rate and pressure down stream from the filter are substantially reduced. This, in turn, causes a decrease in system performance and an increase in operating costs.
Pumps used in aquariums are generally magnetic drive pumps. Submersible magnetic drive pumps (e.g., as available from Horvath) are used extensively inside the aquarium. The Horvath-type pump and the submersible pumps commercially available today differ only in the following:—the submersible pump has a sealed stator assembly and the 90° exit for the pressurized stream is straight. Pumps used outside of the tank or in chemical/food processing have a permanent magnet embedded in the impeller. The impeller is encased, on bushings, in its housing and it is driven by coupling the encased magnet with a motor driven magnet. The motor driven magnet is outside the housing so there are no seals. This type of pump is used to prevent fluid from leaking out of the drive shaft seals or to prevent contamination of the fluid from bearing grease, and so on. The magnetic drive pumps are quiet, reliable and almost never leak. The main drawback to these pumps is the weak coupling between the magnets. The magnetic coupling cannot transfer motor torque to the impeller efficiently. These pumps rely on impeller speed to transfer energy to the fluid and they generally have a high flow, low pressure (3 to 30 psi) discharge. Small changes in motor speed, from minor voltage fluctuations, causes significant changes in the pump output. While this type of pump recirculates water and low viscosity fluids without any problem, it has little value for high viscosity fluids. For the work they perform, magnetic drive pumps consume more power than direct drive pumps.
As mentioned above, the dissipation of energy stored in the fluid stream causes turbulence in the tank. Because energy stored in a fluid stream is proportional to pressure, pumps with a low pressure discharge generally store little energy. While the flow from magnetic drive pumps may seem substantial, the energy is dissipated rapidly, through shear, into the stationary fluid and its effect over the entire tank is minimal. Most of the turbulence occurs near the pump discharge or at the boundaries of the fluid stream.
Since fluid at a high flow rate and high pressure creates the most amount of turbulence, high-pressure/high-volume pumps are the drivers for fast and efficient mixing and processing of fluids. High-pressure/high-volume pumps are also the drivers for creating high amplitude waves in aquariums or cleaning the pores of media used in filters.
Mixers for a slurry or solids, such as beaters, food processors, blenders and so on, all rely on a rotating impeller(s) (e.g., beaters, chopping blades, whisks and the like) to perform mixing, blending, chopping, and so on. Some devices rotate the mixing bowls under the mixing head. The mixers operate by spinning the impeller at a high speed and relying on gravity, centrifugal force and pressure from the impeller to mix the ingredients. The larger the impeller diameter, the more torque is required to mix the ingredients. Most commercial and industrial mixers are scaled such that container size, bowl size, tank size and so on, are chosen after the impeller and motor size has been determined. Most mixers use a bowl that is slightly larger than the impeller diameter so the mixing head will be close to the boundaries of the bowl and the mixing will be automatic. If the user needs to mix a large volume, a larger bowl or container is needed or multiple batches must be prepared. With the larger container, the user is forced to move the container around on the stationary impeller, move the mixer or stop the motor and move the unmixed ingredients toward the impeller. With multiple batches, more mixers or an increased preparation time is required.